Recycle of transalkylation effluent fractions enriched in trimethylbenzene

Abstract

Methods are disclosed for producing C 8 aromatic hydrocarbons. Representative methods comprise fractionating a transalkylation effluent, exiting a transalkylation reaction zone and comprising C 8 and C 9 aromatic hydrocarbons, to provide a C 8 aromatic hydrocarbon-enriched fraction and a C 9 aromatic hydrocarbon-enriched fraction. The methods may further comprise (i) recycling the C 9 aromatic hydrocarbon-enriched fraction to the transalkylation reaction zone and/or (ii) separating, in a xylene separation zone, isomers of C 8 aromatic hydrocarbons in the C 8 aromatic hydrocarbon-enriched fraction, into a para-xylene-enriched extract and a para-xylene-depleted raffinate. Performance in the transalkylation reaction zone is improved and/or downstream processing requirements in an aromatics complex are mitigated.

1 . A method for producing C 8  aromatic hydrocarbons, the method comprising:
 (a) fractionating a transalkylation effluent, exiting a transalkylation reaction zone and comprising C 8  and C 9  aromatic hydrocarbons, to provide a C 8  aromatic hydrocarbon-enriched fraction and a C 9  aromatic hydrocarbon-enriched fraction; and   (b) recycling the C 9  aromatic hydrocarbon-enriched fraction to the transalkylation reaction zone.   
     
     
         2 . The method of  claim 1 , wherein step (a) comprises:
 (a1) fractionating the transalkylation effluent in a benzene column to provide a benzene-enriched fraction, as a low boiling fraction of the benzene column, and a benzene column product, as a high boiling fraction of the benzene column;   (a2) fractionating the benzene column product in a transalkylation product fractionator to provide a toluene-enriched product, as a low boiling fraction, the C 8  aromatic hydrocarbon-enriched fraction, as a medium boiling fraction, and the C 9  aromatic hydrocarbon-enriched fraction, as a high boiling fraction of transalkylation product fractionator.   
     
     
         3 . The method of  claim 2 , wherein the transalkylation product fractionator is a divided wall distillation column. 
     
     
         4 . The method of  claim 1 , wherein step (a) comprises:
 (a1) fractionating the transalkylation effluent in a benzene column to provide a benzene-enriched fraction, as a low boiling fraction of the benzene column, and a benzene column product, as a high boiling fraction of the benzene column;   (a2) fractionating the benzene column product in a toluene column to provide a toluene-enriched product, as a low boiling fraction of the toluene column, and a transalkylation product, as a high boiling fraction of the toluene column; and   (a3) fractionating the transalkylation product in a first xylene column to provide a C 8  aromatic hydrocarbon-enriched fraction, as a low boiling fraction of the first xylene column, and a C 9  aromatic hydrocarbon-enriched fraction, as a high boiling fraction of the first xylene column.   
     
     
         5 . The method of  claim 4 , further comprising separating, in a xylene separation zone, isomers of C 8  aromatic hydrocarbons in the C 8  aromatic hydrocarbon-enriched fraction, into a para-xylene-enriched extract and a para-xylene-depleted raffinate. 
     
     
         6 . The method of  claim 5 , wherein a xylene separation zone combined feed comprises:
 (A) the C 8  aromatic hydrocarbon-enriched fraction, and   (B) a fraction of (i) an isomerate product comprising trimethylbenzene and tetramethylbenzene, and (ii) a reformate splitter fraction.   
     
     
         7 . The method of  claim 6 , wherein a second xylene column provides, as a low boiling fraction, the fraction of (i) and (ii). 
     
     
         8 . A method for producing C 8  aromatic hydrocarbons, the method comprising:
 (a) fractionating a transalkylation effluent, exiting a transalkylation reaction zone and comprising C 8  and C 9  aromatic hydrocarbons, to provide a C 8  aromatic hydrocarbon-enriched fraction and a C 9  aromatic hydrocarbon-enriched fraction; and   (b) separating, in a xylene separation zone, isomers of C 8  aromatic hydrocarbons in the C 8  aromatic hydrocarbon-enriched fraction, into a para-xylene-enriched extract and a para-xylene-depleted raffinate.   
     
     
         9 . The method of  claim 8 , further comprising recycling the C 9  aromatic hydrocarbon-enriched fraction to the transalkylation reaction zone. 
     
     
         10 . The method of  claim 8 , wherein a methylated aromatic hydrocarbon-enriched fraction is reacted in the transalkylation reaction zone to provide the transalkylation effluent. 
     
     
         11 . The method of  claim 10 , wherein the methylated aromatic hydrocarbon-enriched fraction is a trimethylbenzene-enriched fraction obtained from fractionating the feed stream, and wherein the feed stream comprises C 9  and C 10  aromatic hydrocarbons. 
     
     
         12 . The method of  claim 11 , wherein the trimethylbenzene-enriched fraction is obtained as a side cut product of an A9 divided wall distillation column for fractionating the aromatic hydrocarbon-containing feed stream. 
     
     
         13 . The method of  claim 12 , further comprising fractionating a C 10  aromatic hydrocarbon-enriched fraction of the A9 divided wall distillation column, to provide a tetramethylbenzene-enriched fraction. 
     
     
         14 . The method of  claim 10 , wherein the methylated aromatic-enriched fraction is a tetramethylbenzene-enriched fraction obtained from fractionating a feed stream, and wherein the feed stream comprises C 10  aromatic hydrocarbons. 
     
     
         15 . The method of  claim 14 , wherein the tetramethylbenzene-enriched fraction is obtained as a side cut product of an A10 divided wall distillation column for fractionating the aromatic hydrocarbon-containing stream. 
     
     
         16 . The method of  claim 8 , wherein step (a) comprises:
 (a1) fractionating the feed stream comprising C 9  and C 10  aromatic hydrocarbons, to provide a trimethylbenzene-enriched fraction, a trimethylbenzene-depleted fraction, and a C 10  aromatic hydrocarbon-enriched fraction;   (a2) fractionating the C 10  aromatic hydrocarbon-enriched fraction to provide a tetramethylbenzene-enriched fraction, a tetramethylbenzene-depleted fraction, and a heavy aromatics fraction   and wherein step (b) comprises:   (b) reacting the trimethylbenzene-enriched fraction and the tetramethylbenzene-enriched fraction in the transalkylation reaction zone to provide the transalkylation effluent comprising the C 8  aromatic hydrocarbons.   
     
     
         17 . The method of  claim 16 , further comprising:
 (c) producing trimethylbenzene and tetramethylbenzene by isomerizing the trimethylbenzene-depleted fraction and the tetramethylbenzene-depleted fraction in an isomerization reaction zone to provide an isomerization effluent comprising the trimethylbenzene and tetramethylbenzene.   
     
     
         18 . The method of  claim 17 , wherein the trimethylbenzene-depleted fraction, the tetramethylbenzene-depleted fraction, and a para-xylene-depleted raffinate from a xylene separation zone are reacted in the isomerization reaction zone. 
     
     
         19 . The method of  claim 17 , further comprising dehydrogenating, in a dehydrogenation reaction zone, C 9  and C 10  naphthenic hydrocarbons in the isomerization effluent. 
     
     
         20 . A method for producing C 8  aromatic hydrocarbons, the method comprising reacting a C 7  aromatic hydrocarbon and a C 9  aromatic hydrocarbon in a transalkylation reaction zone to provide a transalkylation effluent comprising the C 8  aromatic hydrocarbons, wherein the C 9  aromatic hydrocarbon is present in a C 9  aromatic hydrocarbon-enriched fraction of the transalkylation effluent, which is recycled to the transalkylation reaction zone.